J Obstet Gynecol India Vol. 56, No. 3 : May/June 2006 Pg 212-215

ORIGINAL ARTICLE The Journal of and Gynecology of India

Ultrasonic obstetric conjugate measurement : a practical pelvimetric tool

Bathla Sonal, Rajaram Shalini, Singh Kishore Chandra, Goel Neerja

Department of Obstetrics and Gynecology, Guru Teg Bahadur Hospital and University College of Medical Sciences, Delhi

OBJECTIVE(S): To assess obstetric conjugate ultrasonically at term in the labor room setting, and to study its relationship with mode of delivery, maternal height and neonatal weight. METHOD(S): Fifty-five women at term, in early labor or admitted for induction of labor, entered the study. Longitudinal ultrasonic scanning by transabdominal 3.5 MHz curvilinear probe was performed for measurement of obstetric conjugate from a site most adjacent to to the sacral promontory. Based on this obstetric conjugate measurement, women were divided into three groups namely those with obstetric conjugate < 10 cm, 10.1-12 cm, and > 12 cm. Mode of delivery was noted and maternal height and neonatal weight were correlated with ultrasonic obstetric conjugate. Ordinary least square method and logistic regression analysis were used for statistical analysis. RESULTS: The mean age of the women was 22.65 ± 3.14 years and mean height 149.11 ± 6.72 cm. The cesarean delivery rate was 50%, 3.12%, and 11.7% when ultrasonic conjugate was < 10 cm, 10.1-12 cm, and >12 cm respectively. A positive relationship was found between maternal height and obstetric conjugate. Results from regression analysis show that maternal height determines ultrasonic obstetric conjugate significantly (P <0.001). A good relationship between neonatal weight and ultrasonic obstetric conjugate was also obtained (P < 0.001), with an elasticity of 0.47. CONCLUSION(S) : Ultrasonic obstetric conjugate measurement is a simple, noninvasive and safe method of assessing the anteroposterior diameter of the . An ultrasonic obstetric conjugate of less than 10 cm should alert the obstetrician for a possibility of cesarean delivery.

Key words : pelvimetry, ultrasonic obstetric conjugate, cesarean delivery, maternal height

Introduction imaging (MRI) for pelvimetry carries no radiation exposure but is expensive, time consuming, technically demanding, Normal morphological features of the maternal are and not suitable during labor 3. The ultrasonic measurement an important prerequisite to vaginal delivery. Clinical of obstetric conjugate (UOC) is stated to be simple, cost- evaluation and radiopelvimetry are the accepted methods effective, and clinically useful in women with suspected of evaluation of the maternal pelvis. But, while the clinical inlet contraction 4. The utility of ultrasound pelvimetry method is associated with a subjective error, has been determined in the present study. radiopelvimetry is cumbersome and associated with radiation hazard to the fetus 1,2. Magnetic resonance Method

Paper received on 06/05/2005 ; accepted on 22/01/2006 A prospective nonrandomized study was done on 55 women at term admitted to the labor ward in early labor or for Correspondence : Dr. Gupta Nirmal induction of labor from August 2000 to January 2001. The 246, Anasagar Circular Road, Vaishali Nagar hospital ethical committee had approved the study and Ajmer 305006 informed consent was obtained from the women. Tel. (0145) 2644375 Mobile : 982923390 Email : [email protected] Forty consecutive primigravidas and 15 multigravidas with

212 Ultrasonic obstetric conjugate measurement abnormal presentation, doubtful clinical pelvimetry square method and logistic regression analysis, and a findings, and previous cesarean section or history of correlation between these parameters was attempted. previous difficult delivery were included in the study. Each woman was subjected to clinical and ultrasound Results examination. Age, height, parity, and clinical pelvimetry The age of the women ranged between 18 and 30 years with findings were noted. Depending upon height, women were a mean of 22.65 ± 3.14 years. 10.9% were teenagers. divided into 3 groups i.e., height < 140 cm, between 141 Primigravidas constituted 72.73% (40/55). Out of 15 and 150 cm, and > 151 cm. multiparas five had doubtful clinical pelvimetry findings, four had previous cesarean delivery, one was admitted with breech A transabdominal ultrasonic scan was done using Logic presentation, and five had a history of a previous difficult TM 500MRS PLUS (WIPRO GE) ultrasound machine. A 3.5 delivery. The height of the patients ranged between 135 and MHz transabdominal curvilinear probe was used for the 166 cm with a mean of 149.11 ± 6.72 cm. The UOC varied measurement of the obstetric conjugate. Longitudinal from 9.4 to 12.9 cm with a mean of 11.4 ± 1.07 cm. The tomographic imaging was performed at a site most adjacent distribution of women into Groups A, B and C was 10.9% to the pubic symphysis above the pubic bone on left or (6/55), 58.18% (52/55), and 30.9% (17/55) respectively. right side. A radial acoustic shadow with a bright echo at the superior periphery of pubic bone was observed. The The cesarean delivery rate was 10.9% (6/55) while the internal end of the superior periphery of pubic bone to forceps delivery rate was 5.4% (3/55). Forty-six women sacral promontory was measured as the UOC as described had a normal vaginal delivery. Cesarean delivery for by Katanozaka et al 4 (Figure 1). dystocia recorded in groups A, B and C was 50% (3/6), 3.12% (1/32), and 11.7% (2/17) respectively (Figure 2) i.e., 50% of woman with UOC < 10 cm had to undergo cesarean delivery which was much higher than the cesarean delivery rate in the other two groups. But the number of cesarean deliveries was too small for arriving at statistical significance.

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0 < 10 cm > 12 cm Figure 1. Ultrasound picture showing bright acoustic shadow of pubic symphysis, sacral promontory, ultrasonic obstetric Figure 2. Obstetric conjugate and cesarean delivery. conjugate, and biparietal diameter entering pelvic inlet.

Regression analysis was carried out to examine the relationship Based on the obstetric conjugate measurement, women were between maternal height and obstetric conjugate. Maternal divided into three groups viz., A B and C having UOC < 10 height correlated linearly with UOC (Figure 3). Results from cm, 10.1-12 cm, and > 12 cm respectively. The mode of regression analysis show that maternal height determines delivery, indication for cesarean section when needed, and UOC significantly at 1% level of significance (P < 0.001), birth weight were recorded. which means that a 10% change in maternal height would change UOC by 10.1%. In patients with UOC less than 10 The relationships between obstetric conjugate and mode of cm the likelihood of having a cesarean delivery was 50% but delivery, and maternal height and were evaluated statistical significance could not be derived, as the numbers statistically. Statistical methods used were ordinary least undergoing cesarean section in different group were small.

213 Bathla Sonal et al

A relationship between birth weight and UOC was determined less than 12 cm 6. When both diameters are contracted the and a linear correlation was seen (P < 0.001) (Figure 4). A obstetric difficulty further increases. Cesarean section rate 10% change in UOC influences neonatal weight by 4.7%. in women with obstetric conjugate < 10 cm was higher i.e. The mean weight of the neonates was 2.77 ± 0.35 kg and 50% (3/6) vs 6.1% (3/49) than that with obstetric conjugate there was no perinatal mortality or morbidity. > 10 cm. Katanozaka et al 4 report a 50% incidence of cesarean delivey in women with obstetric conjugate less than 16 12 cm and 7.1% in those with obstetric conjugate more than 14 or equal to 12 cm. The probable reason for this difference 12 from our study might be racial or due to a disparity in birth weight in the two studies. Statistical significance between 10 UOC and cesarean section rate could not be derived because 8 of the small number of women undergoing cesarean section 6 in our study (6/55). An exploration into this issue requires expansion of sample size. The mean ultrasonic obstetric 4 conjugate in our study is 11.4 ± 1.07 cm while that reported 2 by Katanozaka is 12.90 ± 0.88 cm. Ultrasonic obstetric conjugate (cm) conjugate obstetric Ultrasonic 0 125 135 145 155 165 175 It is conventionally said that a smaller woman is likely to have a smaller pelvis 7. Height has been correlated with Maternal height (cm) pelvic size and employed to predict cephalopelvic 8-10 Figure 3. Relationship of ultrasonic obstetric conjugate with disproportion by other workers also . However some maternal height. authors have said that maternal height is a poor predictor of cephalopelvic disproportion 11.

Obstetric conjugate also influenced birth weight to some extent. Birth weight was lower in women with a smaller 4 UOC. Although this finding suggests an indirect influence of maternal size on birth weight, no definite conclusion can be 3.5 drawn, as birth weight is dependent on a number of other 3 variables. 2.5 Conclusion 2 Evaluation of UOC is a simple, feasible, noninvasive, and 1.5 inexpensive method to assess pelvic inlet. It assists in making

1 rational decision about the mode of delivery in many cases. Baby’s birth weight (kg) weight birth Baby’s 0.5 Ultrasonic conjugate measurement would be valuable in cases of suspected inlet contraction, nonprogress of labor with 0 failure of the head to descend, previous prolonged labor, and 8 9 10 11 12 13 14 prior cesarean birth. It can be done at the bedside of the Ultrasonic obstetric conjugate (cm) laboring woman and does not involve radiation exposure. Figure 4. Birth weight vs ultrasonic obstetric conjugate. References Discussion 1. Barton JJ, Garbaciack JK Jr, Ryan GM Jr. The efficacy of x-ray pelvimetry. Am J Obstet Gynecol 1982;143:304-11. Contracted pelvis and cephalopelvic disproportion involving 2. Havery EB, Boice JD Jr, Honeyman M et al. Prenatal x-ray exposure an absolute or relative mechanical disparity between the fetal and childhood cancer in twins. N Engl J Med 1985;312:541-5. size and birth canal continue to be a serious cause of maternal and perinatal morbidity and mortality 5. The best preventive 3. van Loon AJ, Mantingh A, Serlier EK et al. Randomized controlled trial of magnetic resonance pelvimetry in breech presentation at measure for contracted pelvis associated morbidity and term. Lancet 1997;350:1799-804. mortality is timely cesarean section. The pelvic inlet is 4. Katanozaka M, Yoshinaga M, Fuchiwaki K et al. Measurement of considered to be contracted if its shortest anteroposterior obstetric conjugate by ultrasonic tomography and its significance. diameter is less than 10.0 cm and the transverse diameter is Am J Obstet Gynecol 1999;180:159-62.

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5. Abou-Zahr C, Wardlaw T, Stanton C et al. Maternal mortality. World 9. Maternal anthropometry and outcomes. A WHO Health Stat Q 1996;49:77-87. collaborative study. Bull World Health Organ 1995;73(suppl):1- 98. 6. Cunningham FG, Gant NF, Leveno KJ et al. William’s Obstetrics 21st edn. New York; McGraw Hill. 2001:436. 10. Moller B, Lindmark G. Short stature: an obstetric risk factor? A comparison of two villages in Tanzania. Acta Obstet Gynecol Scand 7. van Roosmalen J, Brand R. Maternal height and the outcome of 1997;76:394-7. labor in rural Tanzania. Int J Gynaecol Obstet 1992;37:169-77. 11. Liselele HB, Boulvain M, Tshibangu KC et al. Maternal height and 8. Dajardin B, van Cutsem R, Lambrechts T. The value of maternal external pelvimetry to predict cephalopelvic disproportion in height as a risk factor to dystocia: a meta-analysis. Trop Med Int nulliparous African women: a cohort study. BJOG;2000:107:947- Health 1996;1:510-20. 52.

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